triad vs trilogy

triad and trilogy both are nouns.

Word	Noun	Adjective	Verb	Adverb
triad	Yes	No	No	No
trilogy	Yes	No	No	No

As nouns, trilogy is a hyponym of triad; that is, trilogy is a word with a more specific, narrower meaning than triad:

triad: a set of three similar things considered as a unit
trilogy: a set of three literary or dramatic works related in subject or theme

Other hyponyms of triad include trigon, triplicity.

triad (noun)	trilogy (noun)
a three-note major or minor chord; a note and its third and fifth tones	a set of three literary or dramatic works related in subject or theme
three people considered as a unit
a set of three similar things considered as a unit
the cardinal number that is the sum of one and one and one